Diamines are an important group of chemicals which are used in a wide variety of ways as starting materials, intermediates or end products.
3-Dimethylaminopropylamine (DMAPA, N,N-dimethyl-1,3-diaminopropane), in particular, is an important intermediate for the industrial production of, for example, liquid soaps. In addition, DMAPA serves as starting material for the preparation of coagulants and is even said to have anticorrosive properties.
Diamines, like their amine analogues, are frequently prepared by reduction of nitriles. This reaction is particularly advantageous when primary amines are to be obtained.
The corresponding nitrites, which may already have an amino function, are obtained, for example, from alkenyl nitriles by addition of a monoamine onto the C—C double bond.
It is particularly advantageous if an integrated production process or an integrated apparatus can be used for the preparation of diamines from nitriles. Here, the product stream obtained first, which comprises the amino nitrile, is used directly or after purification for conversion into the diamine in a further step.
Here, the quality of the aminoalkyl nitrile product stream from the first reaction (monoamine and alkenyl nitrile) is of critical importance for the reduction reaction of the nitrite, especially for the consumption of the catalyst used in the reduction.
In the case of 3-dimethylaminopropylamine, the preparation of 3-dimethylaminopropionitrile (DMAPN) is therefore important, with the latter being prepared from acrylonitrile and dimethylamine. The literature describes integrated processes, in particular for preparing DMAPA, which comprise both the addition step and the reduction step. Furthermore, optimized processes are described for each of the individual steps.
These processes can be divided firstly into processes which are carried out batchwise or at least semibatchwise and processes which can be carried out in a continuous mode of operation.
An integrated production process by means of which, for example, DMAPA can be prepared batchwise is described in the German patent application having the application number 10 2005 052 457.5, which was filed by the applicant.
However, it has been found to be advantageous to provide continuous processes as an alternative to such at least partly batchwise processes. Here, it is particularly important to provide a process for the first step which is optimized for the second (reduction) step so that optimized diamine production is likewise obtained in the second (reduction) step.
In this context, a high degree of optimization means, in particular, that a high individual or total yield of diamine is achieved. In addition, it is important for the yield to be achieved with a very high individual or total conversion. Furthermore, another quality criterion is the space-time yields with which such a process can be carried out. Finally, the consumption of the catalyst used in the reduction also plays an important role.
A process for preparing 3-dimethylaminoproprionitrile is described, for example, in DD-A 58 306. In this, it is proposed that previously formed 3-dimethylaminopropionitrile be used as solvent and diluent in the reaction of acrylonitrile with dimethyl-amine in order to achieve, owing to the exothermic reaction and the boiling behavior of dimethylamine, a required improved heat distribution and removal. This is said to increase the yield of 3-dimethylaminopropionitrile.
DD-A 222 011 describes a process for the continuous preparation of DMAPN, in which the reaction components are, in the liquid state, firstly placed in a mixing chamber in a tube reactor and then mixed stepwise and reacted stepwise over the total length of the reactor.
Finally, DE-A 27 09 966 describes the preparation of DMAPN, but in this the dimethylamine is used in gaseous form and the reaction is carried out in a bubble column reactor in which the reactants are conveyed in countercurrent.
Although optimized processes are known in the prior art, there is still a need to provide further processes and corresponding apparatuses in order to optimize the preparation of an aminoalkyl nitrile and/or the resulting preparation of a diamine.